290 CEMENT MATERIALS AND INDUSTRY. Lbull. 
a finely granular structure, quite distinct in appearance from the slat; 
cement rock. 
In composition the limestones commonly used will cany from 90 t 
96 per cent of lime carbonate, with rather less magnesium carbonat 
than is found in the cement rock. All of the cement plants own an 
operate their own cement-rock quarries, but most of them are com 
pelled to buy the pure limestone. When this is the case only ver 
pure grades of limestone are purchased, but when a cement plan 
owns its limestone quarry material running as low as 85 per cent c 
lime carbonate is often used. 
QUARRY PRACTICE. 
In most of the cement-rock quarries of the Lehigh district the roc 
dips from from 15° to 25°, usually to the northwest. At a few quaii 
ries, particularly in New Jersey, the dip is much steeper. The quan 
rics are opened, preferably, on a side hill, and the overlying stripping 
which consists of soil and weathered rock, is removed by scrapers c 
shoveling. The quarry of the Lawrence Cement Company has bee 
extended in its lower levels so as to give a tunnel through which tti 
material is hoisted to the mill. Several other quarries have been ca 
ried straight down, until now they are narrow and deep pits, f roj t 
which the material is hoisted vertically. The Bonneville Portlan 
Cement Company quarry is an extreme example of this t} r pe. 
In quarries opened on a side hill, so as to have a long and rathe 
low working face and a floor at the natural ground level, the rockl 
commonly blasted down in benches, sledged to convenient size f< 
handling and crushing, and carried by horse carts to a point in tl 
quarry, some distance from the face, where the material can be dumpc 
into cars, which are hauled by cable to the mill. . Occasionally tl 
material is loaded at the face into small cars running on temporal;; 
tracks. The loaded cars are then drawn by horses or pushed by im 
to a turntable, where they are connected to the cable and hauled 
the mill. While these methods seem clumsy at first sight, they a 
capable of little improvement. The amount of rock used every day 
a large mill necessitates very heavy blasting, and this prevents pe 
manent tracks and cableways from being laid near to the working fac 
At several quarries the loading into the cars or carts is accomplish if 
by means of steam shovels. The cement rock seems to be w»j 
adapted for handling by steam shovels, but even then much sledgii j 
is necessary, and the blasting operations are interfered with. 
MILL PRACTICE. 
What may be considered as t}^pical American practice in the mar 
facture of Portland cement from dry materials owes its present si ii 
cess largely to the works of the Lehigh district. Previous to 1 1 
